Detergent composition



June 9, 1942- M. METZIGER EI'AL 2,235,576

} DETERGENT COMPOSITION Filed narcn'ls, 1940 500A ASH l l I l l l 2.5.50 7.5 7016 12.5 150 125 20.0

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Patented June 9, 1942 UNITED STATES PATENT OFFICE DETERGENT COBIPOSITIONMax Metziger and Alfred Long, Joliet, 111., as-

signors to Blockson Chemical 00., Joliet, 111.,

a corporation of Illinois In experiments to develop alkaline cleaning"baths for tin. it was discovered that sodium or 1 The present inventionrelates to cleaning tin surfaces. particularly on food containers, suchas milk cans, pie tins. bread tins. cake tins, meatloaf tins, and thelike. These so-called tins are commonly sheet iron articles with a tincoat, which when new is shiny and uniformly mirrorlike in appearance.

In commercial cleaning of such articles an alkali detergent solution isused. It has long been known that Sl'Ch solutions corrode the tin andproduce spangling, the latter being a crystal growth which destroys themirror-like surface. The spangled surface resembles the frosty-likeappearance of new galvanized iron articles. The appearance of spanglingis an indication that the tin surface is on the way to destruction.Heretofore, many addition agents have been successfully used to inhibitthe corrosion and spangling. Among these, one of the most successful isan alkali metal chromate. usually sodium or potassium chromate, ordichromate in the dry composition before solution in water. These arecommonly provided as solid or dry compositions which are sold to beadded in specified quantity to water, for a commercial cleaning bath,which is commonly heated to 80 C. to boiling temperatures. Dichromate inthe composition. in an alkaline solution becomes chromate. Chromates anddichromates are comprehended within the broader term a chromate.

The primary disadvantage of chromates is an injurious action on thehands. which generally come in contact with the bath in a large numberof establishments where such compositions are used. The amount requiredfor inhibiting effect makes the composition an objectionable one. Thedry compositions commercially have about 5% of sodium chromate, in spiteof the fact that the Kochs Patent No. 1,962,821 sets forth compositionsfrom to 8% where an alkali metal silicate is also present as a part ofthe alkali detergent.

The present invention aims to reduce the chromate content to 3% andpreferably to below 1%, by the addition of anothezwagent which iseffective to cause the lower chromate content to exhibit an inhibitingaction at least equivalent to and better than that of the prior artcommercial chromate-inhibited detergents.

In particular, it is an object of the invention to use alkali-metalsilicofluoride as the said added agent to render a composition withsmall quantities of chromate at least equivalent in inhibiting effect tocompositions with larger quantities of chromate.

l5 compositions ineffective.

45 of the bath.

potassium silicofluoride in the composition, undergoes a change inalkali solution, which change 5 is beneficial to the action of cleaningcompositions. It is known for example, that sodium silicofluoride inalkali solution decomposes into sodium fluoride and a form of silica, asa colloidally suspended silica compound. In experiment- 10 ing withvarious successful compositions in which sodium silicofluoride is aningredient, modifications have been made, limited to the sodiumsilicofiuoride in order to determine why the sodium silicofiuoridefunctions. Omitting it renders the Adding an equivalent amount of sodiumfluoride renders the composition ineffective, showing that the effect isnot attributed to the sodium fluoride formed with the alkali detergent.Also, adding an equivalent of freshly precipitated silica (adding firstacid and then ammonia to a sodium metasilicate) is not the equivalent ofusing the sodium silicofluoride. The same is true with respect to silicagel and silicic acid. When the equivalent amounts :5 of sodium fluorideand freshly precipitated silica were used, the effect was not the sameas with sodium silicofluoride.

Then tests were made to determine whether the sodium silicofluoridelowered the bufier index 3:) of the composition, by adding hydrochloricacid tion. and (2) by adding sodium silicofiuoride to a bath containingthe other ingredients. It therefore appears that silicofluoride mustform one or more kinds or forms of reaction products which are efiectiveonly in the solution where formed. This is confirmed by the fact thatthe cleaning bath must be used with or after agitation to make certainthat any solid or settled ingredients in the bath dissolve in whole orin part at an equilibrium condition for the temperature Inchromate-inhibited detergents containing the products from sodiumsilicofiuoride, a much lower amount of chromate may be used. Acomposition containing 5% chromate without the sodium silicofluoride canbe altered to have but 0.5% chromate without loss of inhibited effect,when 5% to 15% of sodium silicofiuoride is also used, depending upon thecharacter of the alkali. Thus, the bath may be made far less injuriousto the hands, and may be compounded at less cost.

The use of alkali metal silicates is not the equivalent of the sodiumsilicofluoride to reduce the chromate requirements, as will be shown bythe following explanation.

Commercial practice in the use of alkaline detergents is more or lessstandardized at specifying up to and not over 8 ounces of the solidchemical composition per gallon of water, and use at 80 C. to boiling.These requirements have been observed for test purposes, using, however,boiling solutions to standardize on temperature and to maintainagitation. Loss of water in the tests was avoided by use of refluxapparatus. A very severe test has been imposed to define successful andunsuccessful solutions.

Baking tins present a more severe requirement than milk cans, forexample. Milk cans present a polished metallic tin surface. Baking tinswhen new, have such a surface which is not desired by bakers. It acts asa reflective insulation retarding baking. It is customary for bakers toheat-treat new tin-ware to produce an ambercolored bronze-like,so-called burned-on coat, which is believed to be an oxide film. Thismay be produced by heating the new tins in an oven at 375-400 F. forone-half hour to one hour. Bakers not only desire to prevent spanglingof the tin, but also to retain this coat in using alkaline cleaningbaths.

Another feature of a successful composition is the ability to use thebath more than once. In other words, its inhibiting qualities must notvanish early. Freshly made compositions which are successful to cleanand preserve the burnedon coat of a first insert, and which then removethe coat from a following insert, are considered to be unsuccessfulcompositions.

In determining the line between successful compositions and unsuccessfulcompositions, as defined for the present invention, the following testhas been employed.

A bath is prepared in the proportion of 8 ounces of the composition tobe tested to 1 gallon of water. A 100 cc. volume of the solution isheated to boiling under reflux conditions in a glass flask. Test stripsare fresh tinned sheet iron x3 inches with and without burned-on coatingon both sides. These present galvanic couples as well as full-tinnedareas. and the couples introduce electrical forces which the cleaningbath must make non-corrosive in actual effect. One strip is immersed for1 hour. If it is injured the composition is deemed notsatisfactory: Ifit is not injured, another strip is inserted for 5 hours. If it isinjured, the composition is deemed not satisfactory. If it is notinjured, another strip is inserted for 15 hours. If it is injured, thecomposition is deemed not satisfactory. If it is not injured thecomposition is deemed successful and satisfactory.

Upon this basis many compositions have been tested using as theprincipal alkaline agent (1) anhydrous soda ash, (2) crystallinetrisodium phosphate with 12 molecules of water, (3) sodium metasilicate,and (4) a mixture of equal parts of the first three. These are thecommon noncaustic alkaline detergents, although the art is not limitedto them. Various percentages of sodium chromate, and various percentagesof sodium silicofiuoride were present. Since sodium silicofluorideconsumes alkali in the decomposition occurring in tests, change ofalkalinity or alkaline base was avoided by adding also just enoughcaustic soda to supply the alkali consumed.

Fig. 1 represents the limiting lower percentages of sodium chromate andof sodium silicofluoride in the compositions indicated.

At 4% of sodium chromate and with no sodium silicofluoride, where thedetergent is soda ash, or is trisodium phosphate, or is sodiummetasilicate, it is shown that the compositions are satisfactory. Wherethe detergent is the mixture of these three, 1.5% of sodium chromatewith no sodium silicofiuoride, makes a satisfactory composition. It isalso shown that as sodium silicofluoride is added. the amount ofchromate may be reduced. In the case of soda ash. illustrated by linel0. 1.5% of sodium silicofluoride displaces about 0.5% of thecomposition as sodium chromate, and 2.5% of sodium silicofluoridedisplaces about 3% of the composition as sodium chromate, and beyondthis point, the additional silicofiuoride is less efiective. However, 5%of sodium silicofiuoride displaces 3 70 of the composition as sodiumchromate, and 7.5% of sodium silicofluoride displaces 3.7% of thecomposition as sodium chromate.

In the case of trisodium phosphate, the effect of small amounts ofsodium silicofiuoride is shown by line I I to be still more effective indisplacing sodium chromate than in the case of soda ash of line In, butthe effect falls off earlier, and at about 2.5% sodium silicofiuoride,about 2.5% of the composition as sodium chromate is displaced. To reducethe chromate respectively to 1% and 0.5%, the sodium silicofiuoride is7.5 and 15%.

In the case of sodium metasilicate as shown by line I2, theeffectiveness of the sodium silicofluoride is still less, and 2.5% of itdisplaces about 1% of the composition as sodium chromate, and 15% of itdisplaces about 2.5% of the composition as sodium chromate.

In the case of the mixed detergents as represented by line l3, theeffect is much less. However, since this mixture permits of lesschromate when no silicofluoride is present, it may be said morefavorably that this necessary chromate may be cut in half by about 11%of sodium silicofluoride.

EXAMPLES tures may be used, such as Example 1 Per cent Soda ash 19.5Trisodium phosphate, monohydrate Sodium metasilicate 25 Sodiumsilicofiuoride 10 Sodium bichromate 0.5

Example 2 Per cent Soda ash 44.5 Sodium metasilicate Sodiumsilicofluoride 5 Sodium bichromate 0.5

It will be noted that the region where lines I0, I l, and (3 lie closetogether is designated I4, and it corresponds substantially to about1.5% chromate and about 2.5% silicofluoride. For the detergent bases ofthese lines H), II and I3, compositions having at least about 1.5% andless than 4% chromate, and at least 2.5% silicofluoride aresatisfactory, and in them, if the silicofluoride is increased thechromate may be reduced.

It is also observed that in the series of curves,

.after any knee thereof is passed with increasing amounts of thesilicofluoride, the lines are generally parallel, with the slope oflines H and I3 being the approximate slope. According to thisindication, every increase of 1% in the silicofluoride corresponds toabout .0'75% permissible decrease in chromate from a critical lowerlimit according to the test used. This applies generally after thesilicofluoride content reaches 2.5%, showing that this is a criticallower limit for the silicofluoride above which its function is fairlyconstant. At this critical limit, the chromate must be about 1.5% forall the detergents shown, except that it must be about 3% for sodiummetasilicate on curve l2.

It is not necessary to provide the chemicals as a mixture. It ispermitted also to add the silicofluoride as a separate ingredient to abath containing the chromate and alkali, or to contain one or both ofthem. For example, a bath or composition of alkali and chromateinsuificient to inhibit injury, and in excess of 0.3 to 0.5% of thechemicals of the bath, may be made inhibitory by adding sufficientalkali metal silicofluoride as herein disclosed.

Numerous variations of the invention will occur to those skilled in theart from the description and from the illustration, and such arecontemplated as falling within the scope of the appended claims.

We claim:

1. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituent anon-caustic alkaline detergent, less than 4% of a chromate salt ofalkali metal, and an alkali metal silicofluoride up to about 2. Analkaline composition for forming cleaning baths for metal-ware with tinsurfaces comprising as the essential cleaning constituent a non-causticalkaline detergent, from 4% to 1.5% of an alkali metal chromate, and upto 15% of alkali metal silicofluoride, the quantity of chromate beinggreater when the quantity of the silicofluoride is lesser.

3. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituent anon-caustic alkaline detergent, at least 1.5% and n more than 4% oflkali metal chromate, and

at least 15% of alkali metal silicofluoridei 4. An alkaline compositionfor forming cleaning baths for metal-ware with tin surfaces comprisingas the essential cleaning constituent trisodium phosphate, less than 4%and at least 0.5% to 1.5% of alkali metal chromate, and from 15% toabout 2.5% of alkali metal silicofluoride, the higher quantity of thesilicofluoride being used for the lowest quantity of the chromate andthe lower quantity of the silicofluoride being used when there is atleast about 1.5% of chromate.

5. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituentsubstantially equal parts of soda ash, trisodium phosphate and sodiummetasilicate, less than 4% and at least 0.5% to 1.5% of alkali metalchromate, and from 15% to about 2.5% of alkali metal silicofluoride, thehigher quantity of the silicofluoride being used for the lowest quantityof the chromate and the lower quantity of the silicofluoride being usedwhen there is at least about 1.5% of chromate.

6. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituent sodaash, less than 4% and at least from about 0.3% to about 1% of alkalimetal chromate, and from about 7.5% to about 2.5% of alkali metalsilicofluoride, the higher quantity of the silicofluoride being used forthe lowest quantity of the chromate and the lower quantity of thesilicofluoride being used when there is at least about 1% of chromate.

'7. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituent sodaash, less than 4% and at least about 0.3% of alkali metal chromate, andalkali metal silicofluoride up to at least 7.5%, chromate in the rangeof 3.5% to about 1% corresponding to silicofluoride at least in anamount in the range from 1.5% to 2.5%, and chromate in the range from 1%to 0.3% corresponding to silicofluoride at least in the range from 2.5%to 7.5%.

8. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituent anon-caustic alkaline detergent, at least 2.5% of alkali metalsilicofluoride, and less than 4% and at least from 1.5% to 3% of alkalimetal chromate, the quantity within the said range of 1.5% to 3% beingdependent upon the alkali detergent such that when it is sodiummetasilicate the chromate is at least 3%.

9. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituent anon-caustic alkaline detergent, at least 2.5% of alkali metalsilicofluoride and at least a critical inhibiting amount of alkali metalchromate and less than 4%, the highest critical amount corresponding to2.5% of the silicofluoride, and the said highest critical amount beingreduced by about .075% in the composition for each increment of 1% inthe content of the silicofluoride.

10. An alkaline composition for forming cleaning baths for metal-warewith tin surfaces comprising as the essential cleaning constituent amixture of substantially equal parts of soda ash, trisodium phosphate,and sodium metasilicate; and less than 4% of alkali metal chromate, andup to 15% alkali metal silicofluoride, the lower limit of chromate beingfrom 1.5% to 0.5% accordingly as the silicofluoride varies from 15%.

MAX METZIGER. ALFRED LONG.

